Vulcanizable rubber composition and method of vulcanizing rubber



United rates 2,996,483 VULCANIZABLE RUBBER COMPOSITION AND METHOD OF VULCANIZING RUBBER Lloyd 0. Bentz, Lancaster, Pa., and George E. P. Smith, Jr., Akron, Ohio, assignors to The Firestone Tire 8: Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Original application Dec. 131, '1956, Ser. No. 631,421. Divided and this application May I l, 1959, Ser. No. 817,702

6 Claims.

This invention relates to some unique members of a new class of =benzothiazole sulfenamides and to the application of these substances to accelerating the vulcanization of rubber. 7

During recent years the channel carbon blacks have been increasingly replaced by the newer fine furnace blacks in pneumatic tire tread compositions. The new furnace blacks, designed HAF, ISAF and SAF blacks, have become so popular because they impart much longer tread life to tires than did the channel blacks. Whereas the channel blacks were acidic in reaction, the new furnace blacks are alkaline, displaying pH values above 7.0. Perhaps partly because of their alkalinity the new furnace blacks have been difficult to handle in modern high speed rubber processing equipment, because they tend to make rubber stocks scorchy, the stocks tending to set up or pro-cure before the end of the mechanical working of the stocks during processing in Banbury mixers, mills, calenders and extruders. A scorched stock, of course, must be scrapped.

It is an object of the present invention to provide a new class of vulcanization accelerators comprising benzothiazole sulfenamides possessing unique and valuable rubber vulcanization accelerating characteristics. It is also an object to provide improved rubber compositions free from tendency to scorch during factory processing operations. A further object is to provide an improved method of manufacturing furnace black reinforced rubber compositions. The above and further objects will become apparent in the description of the invention which follows. The objects of the invention are realized by the successful preparation of a new group of closely related benzothiazole sulfenamides and the employment of these new compounds as accelerators of rubber vulcanization. The novel compounds, the benzothiazole sulfenamides of tertiary alicyclic primary amines can be prepared in accordance with the following examples.

EXAMPLE 1 Reactants 5.6 grams (0.033 mole) 2-mercaptobenzothiazole 6.7 grams (0.17 mole) sodium hydroxide in 70 ml. water 20 grams (0.133 mole) l-methylcyclohexylamine hydrochloride 25 ml. ethanol 22.5 ml. 1.69 molar sodium hypochlorite (containing 0.038 mole sodium hypochlorite) Conditions The mercaptobenzothiazole was dissolved in the sodium hydroxide solution, and the amine hydrochloride was added. The resulting two phase liquid mixture was made homogeneous by stirring in the ethanol. Thereafter, the solution was stirred at 2527 C. during addition of the hypochlorite solution gradually over a period of 55 minutes. After an additional minutes of stirring the reaction mixture was filtered. The white crystals, which were so separated, were washed and air-dried.

Patented Aug. 15, 1961 ice Result Yield of 46% N( lmethylcyclohexyl)-2-benzothiazole sulfenamide, of the formula 1 Y C a C 7 Melting at 104-105" C.

Chemical analysis:

Found: 10.23% nitrogen; 22.75% sulfur. Calculated: 10.06% nitrogen; 23.04% sulfur.

EXAMPLE 2 Reactants 5 .6 grams (0.033 mole) Z-mercaptobenzothiazole 1.33 grams (0.033 mole) sodium hydroxide 'in 50 ml. water 13.2 grams (0.133 mole) l-methylcyclopentylamine 22 ml. 1.69 molar sodium hypochlorite (containing 0.037

mole sodium hypochlorite) Conditions The mercaptobenzothiazole and the amine were dissolved in the sodium hydroxide solution. Then the hypochlorite solution was gradually added, with stirring, over a period of 45 minutes. After an additional 30 minutes of stirring, the crystalline product was separated from the reaction mixture by filtration and then was washed and air-dried.

Result Yield of 68% N-( l-methylcyclopentyl)-2-benzothiazole sulfenamide, of the formula Melting at 72-74 C.

Chemical analysis:

Found: 10.76% nitrogen; 24.08% sulfur. Calculated: 10.60% nitrogen; 24.26% sulfur.

Ingredients Rubber (smoked sheets)- HAF carbon black Zinc oxide Antioxidant Sulfur Product of Example 1 Product of Example 2 Table 2 shows the results of the Mooney Scorch tests, made at 265 F., in accordance with the article by' R. Shearer, A. E. Juve and 1H. Musch, India Rubber World, volume 117, pages 2l6219 (1947). The test results are that the rubber stock is not scorchy.

TABLE 2 Rubber Composition A Table 3 sets out the normal physical properties of the stocks cured at 280 F., and Table 4 shows physical properties of stocks after aging 2 days at 212 F. The modulus and tensile results are expressed as pounds per square inch (p.s.i.).

TABLE 3 Normal Properties of Stocks Modulus 300%:

Cure TABLE 4 Aged Properties of Stocks The above data show that the novel sulfenamides of the examples are excellent delayed-action accelerators, producing natural rubber tire treads having. high physical properties, which are substantially maintained after the drastic aging treatment of 2 days in air at 212 F. Table 2 shows that the usually scorchy furnace black natural rubber tread stocks were not sco-rchy when accelerated by the sulfenamides of the invention. Therefore, the: new sulfenamides make it possible to utilize the superior reinforcing furnace blacks in natural rubber, without the usual danger of ruining the stocks by scorching during tread extrusion and other processing steps.

The sul-fenamides of the invention are valuable accelerators for the vulcanization of all sulfur-vulcanizable synthetic rubbers, including for example the synthetic natural rubbers, rubbery butadiene-styrene copolymers, rubbery butadiene-acrylonitrile copolymers, rubbery polyisoprenes and polybutadienes. For example, the sulfenamide of Example 2 was tested as an accelerator in a tire tread formula based upon LTP G'R-S (a rubbery butadiene-styrene copolymer produced at approximately F. by aqueous emulsion polymerization) which rubber contains approximately 1.25 percent of phenyl-betanaphthylamine as a stabilizer and antioxidant. The tread formula is given in Table 5, normal physical properties on cures at 280 F. are shown in Table 6 and properties after the vulcanized stocks were aged in air for 2 days at 212 F. are given in Table 7. The numerical values are as in the corresponding earlier tables herein.

TABLE 5 Ingredients: C LTP GR-S 100 HAF carbon black j 48 Processing oil 8 Zinc oxide 3 Stearic acid 2 Phenyl-beta-naphthylamine 0.6 Sulfur 2.0 Product of Example 2 1.2

TABLE 6 Normal properties of stock:

7 Modulus 300%- V C 30' cure No cure 45' cure u No cure 60' cure 1026 cur 2 050 Modulus 400% V V 30' cure No cure 45" cure No. cure 60' cure 1650 l 90' cure 3075 Tensile strength- 30' cure No cure 45' cure .No cure 60' cure 3275 v 90' cure .3525 Elongation (percent)- 30' cure No cure a 45' cure No cure a 60, cure-- r 650 9.0".cure 455 I TABLE 7 Aged properties of stock:

- 'Modulus 300%.r t a C r- -60.' cure 3275 90' cure Tensile. strengthr 0' 60': cure 3475 90rcure 2400 Elongation (percent) .60. cure 320 90" cure 215 The accelerators of the invention are effective in combination with either free sulfur or with a vulcanizing agent of the sulfur-donor type. Known agents of the latter type sulfides and reaction products of primary amines with excess sulfur. Only a relatively small proportion of the accelerators of the invention are required, on. the order of 0.1% to 10% of the wQight-oftherubber employed.

Although the fine furnace blacks (of the high abrasion type) are generally employed; in a loading of 40 to 70 parts per hundred of rubber (phr), they have value as a reinforcing agent in the range of 5 to phr. Ordinary vulcanizing temperatures are contemplated by the invention, preferably in the rangeof 260 to 400 F.

I This application is a division of application Serial Num- Ber. 631,421, fi1ed Dec. 31, 1956. I V e i Wha issl im d 1. 'Method of vulcanizing rubber comprising heating a s'ulfur-vulcanizable 'diene rubber and sulfur in admixture 5 with 0.1% to 10% of the weight of the rubber of a sulfenamide of the class consisting of N-(l-methylcyclohexyl) -2-benzothiazole sulfenamide and N-(1-methylcyclopentyl)-2-benzothiazole sulfenamide.

2. Method of vulcanizing rubber comprising heating a sulfur-vulcanizable diene rubber and sulfur in admixture with 0.1% to 10% of the weight of the rubber of N-(lmethylcyclohexyl)-2-benzothiazole sulfenamide.

3. Method of vulcanizing rubber comprising heating a sulfur-vulcanizable diene rubber and sulfur in admixture with 0.1% to 10% of the weight of the rubber of N-(lmethylcyclopentyl)-2-benzothiazole sulfenamide.

4. A vulcanizable composition comprising a sulfurvulcanizable diene rubber, sulfur and 0.1% to 10% of the weight of the rubber of a sulfenamide of the class consisting of N-( l-methylcyclohexyl) -2-benzothiazole sulfenamide and N-(I-methylcyclopentyl)-2-benzothiazo1e sulfenamide.

5. A vulcanizable composition comprising a sulfurvulcanizable diene rubber, sulfur and 0.1% to 10% of the weight of the rubber of N-(1-methylcyclohexy1)-2- benzothiazole sulfenamide.

6. A vulcanizable composition comprising a sulfurvulcanizable diene rubber, sulfur and 0.1% to 10% of the weight of the rubber of N-(1-methy1cyclopentyl)-2- 10 benzothiazole sulfenamide.

References Cited in the file of this patent UNITED STATES PATENTS Howland Aug. 14, 1945 2,814,208 Smith July 4, 1950 

1. METHOD OF VULCANIZING RUBBER COMPRISING HEATING A SULFUR-VULCANIZABLE DIENE RUBBER AND SULFUR IN ADMIXTURE WITH 0.1% TO 10% OF THE WEIGHT OF THE RUBBER OF A SULFENAMIDE OF THE CLASS CONSISTING OF N-(1-METHYLCYCLOHEXYL)-2-BENZOTHIAZOLE SULFENAMIDE AND N-(1-METHYLCYCLOPENTYL)-2-BENZOTHIAZOLE SULFENAMIDE. 